I have a Flame Angel and, up until recently, a Regal Angel. I put dried algae on two clips almost daily. There is also a good amount of green algae on my rock. The Naso loves it too. Hakari also makes a frozen angel food that has sponge, algae, etc in it. My lfs
also sells algae wafers that sink to the bottom. All the herbivores (and omnivores) love them.